Endosseous dental implants must fulfill a basic biomechanical purpose: the support of biting forces. Direct in vivo measurements of biomechanical forces on implants in animal models would assist in evaluating dental implants and their supporting interfacial tissues from basic and clinical standpoints. Part I of the project will measure vertical and lateral components of in vivo forces on pure titanium dental implants in dogs under bridged, free-standing and semi-buried/shielded conditions. Six dogs will receive bilateral implants in healed premolar mandibular extraction sites. Implants will be shielded by bridges from direct forces for 4 months. Force components will then be measured using transducers and recording methods developed under previous support. Raw bite force data will be recorded on tape and signal-processed by computer to extract characteristic bite force parameters such as mean force, rate of loading, duration of bite pulse, etc. Quantitative biomechanical histories for dental implants in three different bridgework conditions in a dog model will therefore be available for study in relation to the human situation and/or other animal models. Part II will employ biomechanical, histological, ultrastructural and surface-analytical methods to investigate relationships between biomechanical factors of implant design and interfacial tissue response. Ten implants of simple geometry and characterized surfaces will be shielded from direct forces post-operatively to allow similar initial interfaces. Five titanium implants will then be loaded twice a week for one month during animal anesthesia by a special loading device; at all other times implants will be shielded by bridges, as will five contralateral implants. A standardized, loading program formulated from data of Part I will be applied to "loaded" implants. Endosseous and permucosal interfaces will be subjected to light and electron microscopic analyses to reveal interfacial histomorphology for "loaded" and "shielded" implants. Post-implantation surfaces of implants will also be examined by SEM. Part II will provide insight into the biological significance of in vivo forces on dental implants in an animal model.